1. Field of the Invention
The present invention relates to a module substrate which is electrically connected to a mother board by soldering, and to a method of producing the same.
2. Description of the Related Art
In recent years, with miniaturization of electronic apparatuses and devices, the mounting density of electronic components such as semiconductor IC, active components, passive components, and so forth mounted onto circuit substrates has progressively increased. In view of the importance of intermediate inspection, convenience of mounting, and so forth, electronic components are sub-assembled onto a module substrate, and thereafter, the module substrate is fixed to a mother board by using joining-means such as soldering or the like (e.g., Japanese Unexamined Patent Application Publication 63-204693 and so forth).
The module substrate, in a conventional technique, comprises a substrate 1 composed of an insulating resin material having a substantially quadrangular shape and a wiring formed from a conductor, and plural end-face through-holes 2 formed in the outer peripheral edge of the substrate 1, in a concave curved-shape, as shown in FIGS. 27 to 30. Each end-face through-hole 2 comprises an end-face opening groove 2A having a semi-circular shape and an end-face electrode 2B formed on the inner wall of the end-face opening groove 2A. In the end-face opening groove 2A, a solder 2C is filled. To the end-face electrode 2B, a wiring 3 on the front surface side of the substrate 1 is connected. The end-face electrode 2B is connected via the wiring 3 to an electronic component 4 provided in the center on the front-surface side of the substrate 1.
The module substrate formed as described above is placed on a mother board 5, and in this state, is heated. Thereby, the solder 2C in the end-face through-hole 2 is melted and adheres to an electrode pad 6 on the mother board 5. Thus, soldering can be performed. As a result, a fillet 7 is formed from the solder in a smooth curved shape between the end-face electrode 2B and the electrode pad 6, as shown in FIGS. 28 and 29.
In the above-described conventional technique, the wiring 3 made of a conductor is provided on the front surface of the substrate 1 in order to connect the electronic component 4 mounted onto the front surface of the substrate 1 to the electrode pad 6 of the mother board 5. In some cases, as the substrate 1, employed is a multi-layered substrate in which a grounding wiring pattern for connecting the electronic component to a ground is provided.
In this case, since the thermal expansion coefficients of the wiring 3 made of a conductor or the like and the resin material forming the substrate 1 are different from each other, warpage, which is curved in the directions indicated by arrows A in FIG. 28, may occur in the substrate 1 when the substrate 1 is worked or heated for soldering. Similarly, in some cases, warpage is generated in the mother board 5. Thus, a gap may be formed between the end-face electrode 2B of the substrate 1 and the electrode pad 6 of the mother board 5.
As a result, even if the solder 2C in the end-face through-hole 2 is melted by heating, the solder 2C takes on a substantially spherical shape due to surface tension, as shown in FIG. 30, so that the solder 2C does not contact the electrode pad 6 of the mother board 5. Thus, there arises the problem that the end-face electrode 2B cannot be connected to the electrode pad 6.
Furthermore, recently, electronic apparatuses and devices have been reduced in thickness, and there has been a tendency for the thicknesses 6f the substrate 1 and the mother board 5 to be decreased. For this reason, warpages of the substrate 1 and the mother board 5 are increased, causing the connection between the end-face electrode 2B and the electrode pad 6 to become inadequate.
Accordingly, it is an object of the present invention to provide a module substrate of which the end-face electrodes can be securely connected to a mother board even if warpage occurs in the substrate or the like, and a method of producing the same.
To achieve the above object, according to the present invention, there is provided a module substrate which comprises a substrate for mounting an electronic component on the front surface side thereof, and end-face electrodes provided in the end-faces defining the outer peripheral edge of the substrate and adapted to be connected to the electronic component.
The end-face electrodes are each provided with a solder to be connected to a mother board provided on the back surface side of the substrate, and the solder is protruded on the back surface side of the substrate.
In the above-described configuration, even if warpage occurs in the substrate, causing a gap between the end-face electrodes of the substrate and the electrode pads of the mother board, the tips of the solders protruding on the back surface side of the substrate securely contact with the electrode pads of the mother board. Accordingly, in this state by melting the solder, the end-face electrodes and the electrode pads are connected to each other, and fillets can be formed between the end-face electrodes and the electrode pads.
Preferably, said substrate is provided with end-face opening grooves each opening at the end-faces of the substrate, said end-face electrodes are provided on the inner walls of the end-face opening grooves, respectively, and said solders each including an electrode facing portion facing the end-face electrode and being disposed in the end-face opening groove, and an protuberant portion provided so as to protrude from the electrode facing portion to the back-surface side of the substrate.
Thus, with the electrode facing portions, the solders can be attached to the end-face electrodes in the end-face opening grooves. With the protuberant portions, the solders can be contacted with the electrode pads of the mother board.
Also preferably, back-surface electrodes connected to the end-face electrodes are each provided on the back-surface side of the substrate in the peripheries of the end-face opening grooves, and the back-surface electrodes are covered with the protuberant portions of the solder, respectively.
Accordingly, by melting the protuberant portions of the solders, the back-surface electrodes and the electrode pads of the mother board can be connected to each other. The end-face electrodes and the electrode pads can be connected to each other via the back-surface electrodes.
Preferably, the end-face opening grooves are each opened in a substantially semi-circular shape at the front-and back-surfaces of the substrate. Thereby, by circularly perforating the substrate, the end-face opening grooves can be easily formed.
More preferably, the solders are each positioned only on the inner side of the substrate with respect to the end-faces thereof. Accordingly, the solders can be accommodated inside of the substrate without protruding from the end-faces of the substrate.
Also preferably, the solders are each positioned on the inner side of the substrate with respect to the end face thereof so as to face the end-face electrode, and moreover, are protruded outward of the substrate with respect to the end-faces thereof.
Accordingly, the solders each positioned on the inner side of the substrate with respect to the end-face thereof can be fixed to the end-face electrode, and moreover, the solder in such a large amount that it cannot be accommodated on the inner side of the substrate with respect to the end-face thereof can be held at a position protruding outward of the substrate with respect to the end-face thereof.
More preferably, the end-face electrodes each comprise a plane electrode formed on the end-face of the substrate, and the solders each having a columnar shape elongating in the thickness direction of the substrate-are fixed to the plane electrodes with a part of the respective solders being protruded on the back-surface side of the substrate.
Thereby, the plane electrodes can be disposed on the end-faces of the substrate without the substrate being perforated or the like. Furthermore, the solders each forming a columnar shape are fixed to the plane electrodes with a part of the respective solders being protruded on the back-surface side of the substrate. Accordingly, even if a gap is generated between the end-face electrodes of the substrate and the electrode pads of the mother board, the tips of the solders can be contacted with the electrode pads of the mother board.
Preferably, the solders are each positioned only on the outer side of the substrate with respect to the end-face thereof.
Thereby, with the solders each positioned on the outer side of the substrate with respect to the end-face thereof, a fillet can be formed between the end-face electrode of the substrate and the electrode pad of the mother board. Thus, the shape and size of the fillet can be confirmed visually, easily. That is, the connection between the end-face electrodes and the electrode pads can be easily confirmed.
According to the present invention, there is provided a method of producing a module substrate comprising a substrate for mounting an electronic component on the front surface side thereof, and end-face electrodes formed in the outer peripheral edge of the substrate and adapted to be connected to the electronic component, the end-face electrodes each being provided with a solder to be connected to a mother board, which comprises the steps of forming the solder into a columnar shape longer than the thickness of the substrate, and providing the solder on the end-face electrode with a part of the solder having the columnar shape being protruded on the back-surface side of the substrate.
Accordingly, the solders each formed into a columnar shape can be fixed to the end-face electrode, and a part of the solder can be protruded on the back-surface side of the substrate. Gaps generated between the end-face electrodes and the electrode pads can be filled with the solders protruding on the back-surface side of the substrate, and the end-face electrodes and the electrode pads can be connected to each other.
Furthermore, there is provided a method of producing a module substrate comprising a substrate for mounting an electronic component on the front surface side thereof, and end-face electrodes provided in the outer peripheral edge of the substrate and adapted to be connected to the electronic component, the end-face electrodes each being provided with a solder to be connected to a mother board, which comprises the steps of: forming a plurality of through holes in line in a work substrate, forming an electrode film on the inner wall of each through hole, placing the work substrate on a jig having a plurality of holes having bottom in line such that the through holes are aligned with the holes having bottom, respectively, supplying the solders into the through holes and the holes having bottom so as to be fixed, respectively, cutting the work substrate and the jig along the lines passing through the centers of the respective through holes, and removing the jig from the work substrate, whereby the solders are each provided on the inner side of the substrate with respect to the end-face thereof.
Accordingly, the work substrate having a plurality of through holes formed therein can be placed on the jig, so that the through holes of the work substrate can be aligned with the holes having bottom of the jig, respectively. Furthermore, after the solders are placed into the through holes and the holes having bottom and fixed thereto, the work substrate is cut along the line passing the centers of the through holes. Thereby, the end-face electrodes opening on the end-face side of the substrate can be formed, and by removing the jig, the protuberant portions defined by the solders protruding on the back-surface side of the substrate can be formed.
Moreover, there is provided a method of producing a module substrate comprising a substrate for mounting an electronic component on the front surface side thereof, and end-face electrodes provided in the end faces defining the outer peripheral edge of the substrate and adapted to be connected to the electronic component, the end-face electrodes each being provided with a solder to be connected to a mother board, which comprises the steps of forming a plurality of through holes in line in a work substrate, forming an electrode film on the inner wall of each through hole, forming back-surface electrode films on the back-surface side of the work substrate and being arranged in the peripheries of the respective through holes, forming each of a plurality of solder accommodation holes adjacent to each of the through holes having a semi-circular shape in the work substrate, supplying the solders into the through holes and the solder-accommodation holes from the back-surface side thereof with the front-surface side of the through holes and the solder-accommodation holes is closed, heating the solders to form solder protuberant portions each covering the back-surface electrode, and cutting the work substrate along a line passing through the solder accommodation holes, whereby the solders are each provided on the end-face side of the substrate.
Accordingly, the end-face electrodes and the back-surface electrodes can be formed by forming the solder accommodation holes adjacent to the through holes. Furthermore, the protuberant portions of the solders covering the back-surface electrodes can be provided by supplying the solders into the through holes and the solder accommodation holes from the back-surface side while the front-surface side of the through holes and the solder-accommodation holes is closed, and heating-the solders. By cutting the work substrate along a line passing the solder accommodation holes, the end-face opening grooves opening at the end-faces of the substrate can be provided, and moreover, the solders each including the electrode facing portion and the protuberant portion can be provided in the end-face opening groove.
Furthermore, there is provided a method of producing a module substrate comprising a substrate for mounting an electronic component on the front surface side thereof, and end-face electrodes provided in the outer peripheral edge of the substrate and adapted to be connected to the electronic component, the end-face electrodes each being provided with a solder to be connected to a mother board, which comprises the steps of forming a plurality of through holes in line in a work substrate, forming an electrode film on the inner wall of each through hole, forming back-surface electrode films on the back-surface of the substrate in the peripheries of the through holes, forming each of a plurality of solder accommodation holes adjacent to each of the through holes having a semi-circular shape in the work substrate, cutting the work substrate along a line passing through the solder-accommodation holes, supplying the solders into the through holes and the solder-accommodation holes from the back-surface side thereof with the front-surface side of the through holes and the solder-accommodation holes being closed, and heating the solders to form solder protuberant portions each covering the back-surface electrode, whereby the solders are each provided on the end-face side of the substrate.
Accordingly, the end-face electrodes and the back-surface electrodes can be formed by forming the solder accommodation holes adjacent to the through holes. By cutting the work substrate along a line passing the solder accommodation holes, the end-face opening grooves opening at the end-faces of the substrate can be provided. Furthermore, by supplying the solders into the through holes and the solder accommodation holes from the back-surface side while the front-surface side of the through holes and the solder-accommodation holes is closed, and heating the solders, the protuberant portions of the solders covering the back-surface electrodes can be provided, and moreover, the solders each including the electrode facing portion and the protuberant portion can be provided in the end-face opening groove.